Shunt systems for directing body fluid from one region to another are known in the medical field. One application for such a fluid shunt system is in the treatment of hydrocephalus in order to direct cerebrospinal fluid (“CSF”) away from the brain and into the venous system or to another region of the body. In this application, a shunt is implanted on the patient's skull, under the scalp, and is coupled to a brain ventricle catheter which is adapted for insertion into the brain and to a distal catheter which is adapted for insertion into the drainage region, such as the peritoneal cavity, the atrium or other drainage site.
The shunt systems typically include a pressure-regulated valve to control the flow rate of the CSF. The distal catheter is typically implanted caudal to the ventricular inlet which causes the shunt system to act as a siphon when the patent is in the upright position. The siphoning effect can cause overdrainage that can lead to low pressure headaches, slit ventricles, and subarachnoid hemorrhages.
Anti-siphoning has previously been addressed with several mechanisms, including weighted ball and seat valves, flow control valves, and diaphragm valves. In turn, the weighted ball and seat valves contain one or more balls or other mechanism, that when acted on by gravity, i.e. when the patient is upright, the ball seats in the valve passage and closes the fluid pathway. Closing a primary fluid pathway can lead to underdrainage if the alternate pathway does not provide sufficient drainage as well. Another ball and seat design closes in response to excessive flow, but offers a secondary pathway that always remains open, allowing for constant drainage, but the resistance of the secondary pathway remains fixed. Diaphragm valves are typically in the closed flow position and only opening in response to positive pressure and closing again when under negative distal pressure. A diaphragm valve has its disadvantages, in that it can become encapsulated by tissue and fails to open under positive pressure, this leads to underdrainage.
Examples of previous solutions include U.S. Pat. No. 4,605,395 to Rose et al. disclosing a single flow path ball and seat valve and U.S. Pat. No. 4,681,559 to Hooven, having two flow paths, but both have pressure valves. U.S. Pat. No. 6,126,628 Nissels is a pressure valve with a tortuous secondary flow path. However, the secondary flow path has fixed flow characteristics. Additionally, U.S. Pat. No. 8,177,737 to Negre et al. is a pressure valve with numerous secondary ports, but the flow to certain ports is controlled by the location of the ball in the primary flow path. Thus, the need exists for an anti-siphon valve of simple design, yet having multiple flow and pressure characteristics.